@JDallas
The NILES user manual has a couple charts that you need to study a bit and they don’t talk specifically about 6-OHM speakers. Use the 2x setting for your speakers.
Speaker impedance specifications are not very precise. The magnitude of the impedance varies with frequency. By “magnitude” we are specifying what value resistor could replace the speaker at a specific frequency and dissipate the same power as the speaker. Usually, there is a reference to “nominal impedance” on the speaker spec sheet. Unfortunately, this is a judgement call by someone. Some companies give the lowest value, regardless of frequency, other companies will give the magnitude in the 60Hz range, even if the magnitude at some other frequency is lower, The actual magnitude can vary from a few Ohms for frequencies below 100HZ to a few hundred Ohms or more at higher frequencies. There are a few notorious high end speakers that will have a sharp magnitude dip at some low frequency, say 30Hz. These speakers are very hard to drive because an occasional extreme bass note will overload the amplifier. These speakers will usually claim to have a 4-Ohm or 6-Ohm nominal impedance, but at that critical frequency they’ll dip to 2-Ohms or less. Mainstream amplifiers will drive these speakers just fine, until that monster bass note strikes at the critical frequency, then the amplifier will misbehave. The weaker products might even fail. There is a group of high end, expensive amplifiers that are over designed and will tolerate the occasional dip to one or two Ohms. The amplifier designer will brag that his amplifier can deal with notorious speaker xyz. I prefer that xyz would specify a lower nominal impedance and allow the user to more intelligently pick the amplifier.
AMP is well protected and tolerates impedance dips. AMP will perform well with some of these difficult speakers. If the speaker attempts to step out of AMP’s safe zone, AMP will reduce the Volume or shut down. If you use this as a warning, then take corrective action, AMP will not suffer any permanent damage if there are a few transgressions.
I looked at the charts before posting but as you mention they don’t address 6 ohms speakers and I was unsure the effect of having 2 controls. I’ll set both to the 2x setting. Am I correct that the 2x recommendation is based on using the “amplifiers minimum speaker load of 4 ohms” chart with 1 pair of 8 ohm speakers and 1 pair of 4 ohm? I appreciate the input.
The custom of assigning a rating for a speaker’s impedance is a bit too ‘slippery’ for my taste. And, it’s unfortunate that virtually no home or professional installers have proper equipment or skills to measure and interpret speaker impedance implications. Some companies might assign an 8-Ohm rating while other companies might assign a 4-Ohm rating to your 6-Ohm speakers.
Setting the control driving the 6-Ohm pair to 2x will prevent AMP from seeing a total load of less than 4-Ohms. In your situation it is not critical that the 8-Ohm pair is also set to 2x. If you had the capability to measure system load impedance it could easily be possible that the system would be stable with both controls set at 1x.
For a given output I’m sure that the control settings for the speakers will be different for the two pairs. While this may be an annoyance for the operator, it’s not a major concern.
I anticipated the difference in control settings. Most of the time I’ll leave one pair static and adjust the more accessible control as needed to balance the output. Having two controls also allows me to listen to only 1 of the 2 pairs which is helpful. Thanks again!
